1. Field of the Invention
The present invention relates to a transparent substrate which is provided with at least one thin layer that is based on silicon nitride or silicon oxynitride. One application of the invention is the manufacture of so-called functional glazing assemblies used in buildings, vehicles, or as a plasma television screen. Another application which may be envisaged is the surface treatment of glass bottle containers. The invention also relates to a process for depositing these layers using a pyrolysis reaction.
2. Discussion of the Background
Within the context of the invention, the term functional glazing assembly should be understood to mean a glazing assembly in which at least one of its constituent transparent substrates is covered with a stack of thin layers so as to give it particular properties, especially thermal, optical, electrical or mechanical properties, such as scratch-resistance.
As an example, so-called low-emissivity thin layers are typically composed of a doped metal oxide, for example fluorine-doped tin oxide (F:SnO2) or tin-doped indium oxide (ITO), which may be deposited on glass using pyrolysis techniques. Once coated with a low-emissivity layer, the substrate mounted in a glazing assembly, in particular in a building, makes it possible to reduce emission, in the far infrared, to the outside of the room or vehicle interior through the said glazing assembly. By reducing the energy losses due in part to this radiation leakage, the thermal comfort is greatly improved, and particularly in the winter.
Alternatively, the substrate thus covered may be mounted in a double-glazing assembly; the low-emissivity layer being turned towards the gas-filled cavity separating the two substrates, for example, as the 3 face (the faces of a multiple-glazing assembly are conventionally numbered starting from the outermost face with respect to the room or the vehicle interior). The double-glazing assembly thus formed has enhanced thermal insulation, with a low heat-exchange coefficient, K, while maintaining the benefit of solar energy influx, with a high solar factor (i.e. the ratio of the total energy entering the room to the incident solar energy). On this subject, the reader may refer, in particular, to patent applications, EP-0,544,577, FR-2,704,543 and EP-0,500,445.
The low-emissivity layers are generally made of good electrical conductors. This allows the glazing assemblies, by providing suitable current leads, to be used as heating/de-icing glazing assemblies in motor vehicles, which application is described, for example, in EP-0,353,140.
Thin filtering layers, also called selective or anti-solar layers, are known which, when deposited on substrates mounted in a glazing assembly, make it possible to reduce the heat influx from solar radiation through the glazing assembly into the room or vehicle interior, by absorption/reflection. The layers may, for example, be layers of titanium nitride TiN (or titanium oxynitride), such as those obtained using a gas-phase pyrolysis technique and described in patent applications EP-0,638,527 and EP-0,650,938. The layer may also be a thin (less than or equal to 30 nm) reflective layer of aluminum, obtained by condensation of a metal vapor, CVD or the technique described in international patent application PCT/FR-96/00362 filed on Mar. 7, 1996, in the name of Saint-Gobain Vitrage.
The invention also relates to the techniques for depositing these various layers, and more particularly to those involving a pyrolysis reaction. These techniques consist in spraying xe2x80x9cprecursorsxe2x80x9d, for example of an organometallic nature, which are either in the form of a gas, or in the form of a powder, or are liquids by themselves or else in solution in a liquid, onto the surface of the substrate which is heated to a high temperature. On coming into contact with the substrate, the said precursors decompose thereon, leaving, for example, a layer of metal, oxide, oxynitride or nitride. The advantage of pyrolysis resides in the fact that it allows direct deposition of the layer onto the glass ribbon in a line for manufacturing flat glass of the float type, continuously, and also in the fact that the pyrolysed layers have (in general) very good adhesion to the substrate.
The low-emissivity or filtering layers mentioned above frequently form part of a stack of layers and are, at least on one of their faces, in contact with another layer, generally a dielectric material having an optical and/or protective role.
Thus, in the aforementioned patent applications EP-0,544,577 and FR-2,704,543, the low-emissivity layer, for example made of F:SnO2, is surrounded by two layers of dielectric of the SiO2, SiOC or metal-oxide type, which layers have a refractive index and a thickness which are selected so as to adjust the optical appearance of the substrate, in particular in reflection, for example its color.
In patent application EP-0,500,445, also previously mentioned, the low-emissivity layer of ITO lies under a layer of aluminum oxide so as to protect it from oxidation and also, under certain conditions, to avoid having to subject it to a reducing annealing operation and/or to allow the coated substrate to be bent or toughened without adversely affecting its properties.
The TiO2 layer or the TiO2/SiOC double layer which covers the TiN filtering layer in the aforementioned patent application EP-0,650,938 also protects the TiN from oxidation and improves its durability in general.
However, the integrity of the stacks of thin layers is important. Thus, it is necessary for them to display:
the ability to withstand chemical attack. It frequently happens that the transparent substrate, once coated with layers, is stored for quite a long period before being mounted in a glazing assembly. If the coated substrate is not carefully packaged in a sealed, and therefore expensive manner, the layers with which it is coated may be directly exposed to a contaminated atmosphere or may be subjected to cleaning by detergents which are not well suited to removing dust therefrom, even if the substrates are subsequently joined together in a double-glazing assembly or in a laminated glazing assembly with the deposited thin layers as the 2 or 3 face, and therefore protected. Moreover, apart from the storage problem, there is a disincentive to use the substrates as xe2x80x9cmonolithic glazing assembliesxe2x80x9d or to arrange the layers as the 1 or 4 face in the case of multiple glazing assemblies, i.e., configurations in which the layers are exposed all year long to the ambient atmosphere if the stacks are susceptible to chemical corrosion;
the ability to resist mechanical damage. For example, the transparent substrate, once coated with layers, may be used in configurations in which it is readily exposed to scratching damage. Consequently, on the one hand, the substrate no longer has a xe2x80x9ccorrectxe2x80x9d aesthetic appearance, since it is partially scratched, and, on the other hand, the durability of both the stack and the substrate is greatly diminished, because scratching may introduce possible sites of mechanical weakness, depending on the case.
There is therefore a continual search for a stack of layers having improved chemical and/or mechanical durability. However, these improvements must not adversely affect the optical properties of the assembly formed by the substrate and the stack of thin layers.
As mentioned previously, overlayers of dielectric material already exist which protect the underlying layers in the stack. In order to maintain integrity of an assembly that is exposed to intense or lengthy chemical corrosion, and/or to protect the possibly xe2x80x9cweakerxe2x80x9d underlying layers completely, patent application EP-0,712,815 describes a thin layer based on an oxide comprising silicon and a third element, for example a halogen of the fluorine F type, which facilitates the formation of a mixed silicon/aluminum structure.
The layer described above is particularly suitable for use as the final layer in stacks in which the functional layer is of the filtering or low-emissivity type on glazing assemblies, since it may fulfil an optical function such as optimizing the appearance in reflection, and may guarantee a degree of constancy of the appearance of the glazing assemblies over time.
However, the above-described layer is not necessarily capable of resisting mechanical damage, such as scratches, since does not have an extremely high hardness.
It is known that one type of hard thin layer most particularly designed to be durable and stable with respect to mechanical abrasion and/or chemical attack is a thin layer based on silicon nitride which may, as the case may be, contain a certain amount of oxygen and carbon.
Thus, one type of thin layer based on silicon nitride is known, this being deposited on a substrate by a gas-phase pyrolysis technique using two precursors, the silicon-containing precursor being a silane and the nitrogen-containing precursor being either inorganic, of the ammonia type, or organic, of the hydrazine type, in particular methyl-substituted hydrazine.
However, when the deposition is carried out using nitrogen-containing precursors of the ammonia type, the temperatures are too high (greater than 700xc2x0 C.) to be compatible with continuous deposition on a ribbon of silica-soda-lime glass in the chamber of a float bath since, at these temperatures, these standard glasses have not yet reached their dimensional stability.
In addition, the nitrogen-containing precursors of the hydrazine type have a degree of toxicity which makes their industrial application problematic.
It is also known to deposit a thin layer based on silicon nitride by the above-mentioned technique by using not two precursors but only one; one that contains both silicon and nitrogen, e.g., Si(NMe2)4xe2x88x92nHn. However, the deposition rates that may be achieved are too low to exploit the deposition process on an industrial scale. Furthermore, the synthesis of the precursor is relatively complex and therefore expensive, and the respective proportions of the nitrogen-containing and silicon-containing precursor cannot be varied.
In addition, the known thin layers based on silicon nitride have certain drawbacks:
on the one hand, they are not necessarily sufficiently hard and are less durable, in particular when they are vacuum-deposited in order to, for example, endow a substrate provided with this single layer, or with a stack of thin layers comprising this layer, with a scratch-resistance function; and
on the other hand, when they are deposited by pyrolysis, they are absorbent at wavelengths in the visible range, which is deleterious from an optical standpoint.
Accordingly, one object of the invention is thus to remedy the aforementioned drawbacks and to develop a novel thin layer based on silicon nitride or silicon oxynitride having a greater hardness while being very much less absorbent, and capable of forming part of a stack of thin layers, in particular so as to protect the stack of thin layers with respect to chemical attack.
Another object of the invention is to provide a novel process for depositing a thin layer based on silicon nitride or silicon oxynitride using a gas-phase pyrolysis technique which is compatible with continuous deposition on a ribbon of glass in the chamber of a float bath and which allows high deposition rates to be achieved.
These and other objects have been achieved by the present invention, which provides a coated glass substrate covered with at least one thin layer based on silicon nitride or silicon oxynitride.
Thus, the first embodiment of the present invention provides coated glass substrate that includes a glass substrate and at least one thin layer based on silicon nitride or silicon oxynitride, wherein thin layer includes the elements Si, O, N, and C in the following atomic percentages:
The second embodiment of the present invention provides process for depositing a thin layer on a glass substrate that includes gas-phase pyrolyzing at least two precursors onto a glass substrate, wherein at least two precursors include at least one silicon precursor and at least one nitrogen precursor, wherein the nitrogen precursor is an amine.
The third embodiment of the present invention provides an article or glazing assembly that includes a glass substrate coated with a thin layer based on silicon nitride or silicon oxynitride, wherein the thin layer includes the elements Si, O, N, and C in the following atomic percentages:
Surprisingly, this thin layer has turned out to be both very hard, compared to the other known thin layers based on silicon nitride, and very transparent and therefore has a low or zero absorbance at the wavelengths in the visible range: the high Si and N contents show that what is involved is a material which is mostly silicon nitride. By varying the proportions between the minor constituents, C and O, the properties of the layer may be finely adjusted. Thus, by varying the relative proportions of carbon and oxygen, it is possible both, for example, to xe2x80x9cfine tunexe2x80x9d the density and the refractive index of the thin layer so as to endow it with a mechanical hardness and with optical properties which are very useful and desirable. In order to vary the aforementioned relative proportions, this may possibly be accomplished using a gentle oxidizing agent of the CO2 type, for example for optical reasons. This is because carbon and nitrogen have a tendency to increase the refractive index, oxygen having more the opposite effect.
Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description, which is not intended to be limiting unless otherwise specified.
Preferably, the thin layer contains Si, O, N and C in the following atomic percentages: 40-50% Si, 20-56% N, 5-30% O, and 5-30% C.
Preferably, the refractive index of the thin layer is greater than 1.6, in particular between 1.8 and 2.0, more preferably 1.85.
The thin layer may contain other elements in the form of an additive, such as fluorine, phosphorus or boron, preferably in an atomic percentage of between 0.1 and 5%. The layer may also be homogeneous or have a composition gradient through its thickness.
Preferably, the thin layer has a light absorption coefficient AL of less than 2% for a geometrical thickness of 100 nanometers, which optical quality is particularly demonstrated when the said layer is deposited using a gas-phase pyrolysis technique, as explained below.
The thin layer preferably forms part of a stack of thin layers, at least one layer of which is a functional layer having thermal, in particular filtering, solar-protection or low-emissivity properties and/or electrical properties and/or optical properties and/or photocatalytic properties, such as a layer having a mirror function, of the type containing a doped metal oxide, of a metal nitride/oxynitride or of a metal of the aluminum or silicon type. It may also form part of a stack of antireflection layers, acting as the high-index or xe2x80x9cintermediatexe2x80x9d-index layer.
It is preferable to choose, as the doped metal oxide or the metal nitride/oxynitride, fluorine-doped tin oxide F:SnO2, tin-doped indium oxide ITO, indium doped zinc oxide In:ZnO, fluorine-doped zinc oxide F:ZnO, aluminum-doped zinc oxide Al:ZnO, tin-doped zinc oxide Sn:ZnO, the mixed oxide Cd2SnO4, titanium nitride TiN or zirconium nitride ZrN.
Preferably, the thin layer may be located under the functional layer. It may then fulfil, in particular, the role of a barrier layer to the diffusion of ions, especially of alkali metals, and of oxygen from the glass-type substrate, or else the role of a nucleation layer, and/or have an optical role (adjustment of the color, anti-iridescence effect, antireflection effect). In some applications of the plasma-screen type, it may also fulfil the role of a barrier layer to the migration of Ag+ ions from the silver-based functional layers into the glass-type substrate.
Preferably, the thin layer may be located on the functional layer. It may then serve, in particular, as a layer for protecting the functional layer from high-temperature oxidation or from chemical corrosion, as a mechanical protection layer of the scratch-resistant type, a layer having an optical role or a layer improving the adhesion of the upper layer.
Preferably, the thin layer is the only layer covering the substrate and advantageously fulfills a scratch-resistance function. The geometrical thickness of the layer may be very freely adjusted within a very wide preferred range of 5 nm to 5 xcexcm, in particular between 20 and 1000 nanometers, quite a substantial thickness of at least 250 nm being, for example, preferred in order to accentuate the scratch-resistance effect of the substrate provided with the thin layer, a layer having a smaller thickness being generally desired for another functionality (nucleation, adhesion, etc.).
The subject of the invention is also the process for obtaining the above-defined substrate, which process includes depositing the thin layer based on silicon nitride by means of a gas-phase pyrolysis technique (also called CVD) or using at least two precursors, including at least one silicon precursor and at least one nitrogen precursor. According to the process of the invention, at least one nitrogen precursor is an amine.
The choice of such a nitrogen-containing precursor is particularly advantageous: it has sufficient reactivity insofar as it makes it possible to carry out the deposition at temperatures at which the glass substrate of the standard silica-soda-lime type has fully achieved its dimensional stability, in particular in the context of a float-glass production line.
In addition, the deposition rates achieved are sufficiently high to be able to deposit substantial thicknesses in the float chamber.
The silicon-containing precursor chosen is not particularly limiting but is preferably a silane, such as silicon hydride and/or alkyl silane, or a silazane. The silane or silazane may be preferably substituted with hydrogen or an alkyl group or a mixture thereof. The alkyl group may preferably be a C1-24 branched or unbranched or unsaturated alkyl group. More preferably the alkyl group is a C1-6alkyl group.
The amine may be chosen from primary, secondary or tertiary amines, and preferably those with alkyl radicals having from 1 to 6 carbon atoms each.
Thus, the amine may be ethylamine, C2H5NH2, methylamine, CH3NH2, dimethylamine, (CH3)2NH, butylamine, C4H9NH2 or propylamine, C3H7NH2.
The choice of suitable amine for a layer having a given geometrical thickness and/or a given refractive index is easily determined and results from a compromise between a certain number of parameters such as steric hindrance, reactivity, etc.
Preferably, the ratio, in terms of number of moles, of the amount of nitrogen precursor to the amount of silicon-containing precursor is between 5 and 30, and more preferably is equal to 10.
It is preferable to control such a ratio in order to avoid, on the one hand, insufficient incorporation of nitrogen and, on the other hand, any risk of nucleation in the gas phase and consequently any risk of forming powder. The risks of clogging up the device and reductions in production efficiency are thus limited.
Preferably, when it is desired to incorporate an additive, a precursor of the additive independent of the silicon-containing precursor and the amine precursor is chosen. It may, for example, be a fluorinated gas of the CF4 type when the desired additive is fluorine F or an organic phosphate carrier gas of the PO(OCH3)3 type or a gas of the triethylphosphite, trimethylphosphite, trimethylborite, PF5, PCl3, PBr3 or PCl5 type when the desired additive is phosphorus P or boron B. Advantageously, these additives generally allow the deposition rate to be increased.
The deposition temperature is appropriate to the choice of precursors, in particular the amine. Preferably, it is between 550 and 760xc2x0 C., It may preferably be between 600 and 700xc2x0 C., i.e. between the temperature at which the glass, in particular silica-soda-lime glass, is dimensionally stable and the temperature that the glass has on exiting the float chamber.
Advantageously, the variant in which the glass composition of the substrate is suitable for an electronic application is between 660xc2x0 and 760xc2x0 C.,
According to this variant, an advantageous composition may be that described in Application WO 96/11887, the entire contents of which are hereby incorporated by reference. This composition, expressed in percentages by weight, is of the type:
with:
SiO2+Al2O3+ZrO2xe2x89xa670%
Al2O3+ZrO2xe2x89xa72%
Na2O+K2Oxe2x89xa78%
and optionally BaO and/or SrO in the following proportions:
11%xe2x89xa6MgO+CaO+BaO+SrOxe2x89xa630%
with a lower annealing temperature of at least 530xc2x0 C. and an xcex1 coefficient of 80 to 95xc3x9710xe2x88x927/xc2x0C.
Another advantageous composition, drawn from Application FR 97/00498, the entire contents of which are incorporated by reference, is, still in percentages by weight, of the type:
with:
Na2O+K2Oxe2x89xa710%
MgO+CaO+SrO+BaO greater than 11%, preferably  greater than 15%
and a lower annealing temperature of at least 600xc2x0 C., (Another preferred embodiment consists in choosing an Al2O3 content of 5 to 10% and a ZrO2 content of 0 to 5%, keeping the proportions of the other constituents unchanged).
It will be recalled that the so-called lower annealing (xe2x80x9cstrain-pointxe2x80x9d) temperature is the temperature that a glass has when it reaches a viscosity xcex7 equal to 1014.5 poise.
It is preferable to deposit the layer in an essentially inert or reducing atmosphere, for example an N2/H2 mixture containing no or almost no oxygen, continuously on a ribbon of float glass, in the float chamber and/or in a box for control of the oxygen-free inert atmosphere, in order to deposit it further downstream of the float line, possibly at slightly lower temperatures.
The invention thus allows the manufacture of filtering solar-control glazing assemblies with stacks of the type:
glass/TiN and/or ZrN/thin layer according to the invention/SiOC and/or SiO2, the said layer according to the invention making it possible to have a much stronger interface between, on the one hand, the TiN layer and/or the ZrN layer and, on the other hand, the SiOC layer and/or the SiO2 layer. It also makes it possible to provide effective protection of the TiN and/or ZrN from the risk of surface oxidation either on the industrial line after deposition of the SiOC and/or SiO2 layer, or off the industrial line, for example when the substrate provided with the stack of layers, once it has been cut up, undergoes heat treatments of the bending/toughening or annealing type. Advantageously, the layer has a geometrical thickness of between 10 and 50 nanometers, the thin layer according to the invention has a geometrical thickness of between 5 and 20 nanometers and the SiOC and/or SiO2 overlayer has a geometrical thickness of between 30 and 100 nanometers; or else of the type:
glass/Al/thin layer according to the invention, the aluminum reflective layer either having a small thickness (less than or equal to 30 nm) or having a greater thickness when the mirror function is desired, such as that described in the aforementioned international patent application PCT/FR-96/00362, the entire contents of which are hereby incorporated by reference, the thin layer according to the invention having both a role as oxidation-protection agent and a scratch resistance function.
The invention also makes it possible to produce glazing assemblies whose essential functionality is scratch-resistance, i.e. glazing assemblies such as floor slabs and glass furniture in which the glass substrate is coated only with the thin layer based on Si3N4 according to the invention, optionally combined with an anti-iridescence layer.
Advantageously the glass is thus protected from any degradation. The thin layer according to the invention may also be combined with low-emissivity layers using stacks of the type:
glass/SiOC/F:SnO2 or ITO/thin layer according to the invention.
In these stacks, the SiOC sublayer may obviously be replaced by other metal oxides, such as those described in patent application EP-0,677,493, the entire contents of which are hereby incorporated by reference.
The thin layer according to the invention likewise makes it possible to manufacture any type of functional glazing assembly provided with a stack of thin layers, which has high durability and is capable of being toughened and/or bent when the substrate used is a glass substrate.
The invention furthermore makes it possible to produce glazing assemblies for which an anti-fouling function is desired, using stacks of the type:
glass/thin layer according to the invention/TiO2 
In these stacks, the thin layer according to the invention essentially has the role of acting as a barrier layer to the alkali metals migrating from the glass into the layer based on titanium oxide TiO2, the photocatalytic effect of the latter thus being enhanced. In addition, if the thickness of the layer according to the invention is suitable for it to undergo interferential interaction, it also acts as an anti-iridescence layer.
The titanium oxide TiO2 may be mostly in the form of crystallized particles of the anatase type, as described in patent application WO 97/10188, the entire contents of which are hereby incorporated by reference.
However, it may also be in the form of an at least partially crystallized film, such as that described in patent application WO 97/10186, the entire contents of which are hereby incorporated by reference.
Finally, the invention allows the manufacture of emissive screens of the flat-screen type, such as plasma screens. The thin layer according to the invention may then fulfill different functions depending on the nature of the chemical composition of the substrate on which it is deposited, and/or on the location (front or rear face) of this same substrate in the screen and therefore on the nature of the functional layers which are on top of it, such as the electrodes and the luminophores (photophores), components which are essential for the operation of the screen.
Thus, in the case in which the glass substrate is of the xe2x80x9cblocked alkalixe2x80x9d type, i.e. having a composition substantially free of diffusing species of the alkaline type, the thin layer according to the invention very effectively fulfills the essential role of barrier layer to the migration of species diffusing from the upper coatings towards the substrate, in particular from the silver-based electrode.
Likewise, in the case in which the composition of the glass substrate contains alkali metals, it also fulfils the role of barrier layer to their migration.
The invention also applies to the surface treatment of glass-bottle type containers or flasks, the hard layer according to the invention strengthening the said containers, for example with respect to handling operations likely to damage them, whatever the observed relative thickness inhomogeneity of the said layer. The deposition of the hard layer according to the invention may thus be carried out on the external wall of the containers, by mechanically strengthening it, in particular protecting it from impact, but also on the internal wall of the containers so as, for example, to prevent components from leaking out of the substrate.